Conventionally, when handling paper-based certification such as contracts, certification to the effect that the contents have been verified is carried out by having the certifier sign with a ball pen or affix a seal or the like using ink. However, when such paper-based certification becomes unnecessary, since ink or the like has permeated into the paper, there is the problem that it is not possible to delete the text or other markings and reuse the paper.
For this reason, from the viewpoint of effective use of resources, attention has been given in recent years to the use of certification that does not use paper. As conventional examples of an anti-tampering signature system used in creating certification without using paper and an anti-tampering signature method that is executed using this system, an electronic document anti-tampering system and method are disclosed in JP H11-261550A for example. The signatures used by the electronic signature technology used in this electronic document anti-tampering system and method are signatures in which a characteristic quantity is extracted from the electronic data then encrypted using a private key and sent appended to the electronic data. Then, the recipient of the electronic data verifies that the received electronic data has not been tampered with by decrypting the characteristic quantity with a public key and checking that the characteristic quantity of the received electronic data and the decrypted characteristic quantity match.
Furthermore, as a conventional example of certification that does not use paper, a non-contact IC (integrated circuit) certificate having a rewrite display portion is disclosed in JP 2000-313185A. The non-contact IC certificate is displayed in the rewrite display portion of rewritable media. Rewritable media refers to media in which the contents of display data can be written and erased using electric, magnetic, thermal, or other such external factors. Examples of such rewritable media include media that use microcapsules containing toner, media that use liquid crystal such as ferroelectric liquid crystal, and media that use leuco dyes, and the certificates created using these rewritable media are reusable.
However, since it is premised that the certificates of the above-mentioned electronic signature technology are electronic documents, a viewing apparatus is necessary when carrying out certification, and therefore there is a problem that certification cannot be carried out with the medium as a discrete entity.
On the other hand, with rewritable media that display the above-mentioned non-contact IC certificates, since the rewritable medium itself is not provided with a function to certify the recorded display data, there is the problem that a complicated process is necessary in issuing certificates.
The present invention has been devised to solve these issues, and it is an object thereof to provide an anti-tampering signature method for rewritable media that can easily carry out certification with the medium as a discrete entity, an anti-tampering signature apparatus for executing the method, an anti-tampering signature system provided with the apparatus, an anti-tampering signature program for achieving the method, and a computer-readable recording medium for recording the anti-tampering signature program.